In automotive air conditioning systems, a compressor receives low pressure from an evaporator, compresses it to a higher pressure, and sends it back to the evaporator, after it first passes through a condenser, where it is cooled and liquified. After leaving the condenser, the high pressure, liquified refrigerant is first passed through an expansion valve under high pressure and at medium temperature. The expansion valve does as its name suggests, expanding the liquid refrigerant and thereby lowering its pressure and temperature. The expanded refrigerant enters the evaporator and boils to absorb the heat from vehicle cabin air blown over it. Expansion valves may be nothing more than a fixed orifice. In some applications, however, especially those with fixed displacement compressors, it is necessary to use a thermostatic expansion valve, generally referred to as a TXV, for increased efficiency. A TXV responds to the pressure and temperature of the refrigerant entering and leaving the evaporator, so physical proximity to the evaporator inlet and outlet lines is helpful.
The lines to and from the compressor, condenser and evaporator all have to be fluidly connected when the car is assembled, and it is desirable that those connections be capable of being easily detached, as opposed to a permanent weld or the like. This assists in later servicing, as well as in leak testing the various components individually. However, it is necessary that all connections be tightly sealed. Since the TXV must respond to evaporator outlet and inlet conditions, the block that contains the valve internal components provides a convenient structure within which to incorporate the connectors that join the evaporator lines to the rest of the system. Often, threaded hose fittings have been used, one at the end of each line to be connected, which are threaded into or onto the block. An example can be seen in co assigned U.S. Pat. No. 4,342,421. These have the disadvantage of requiring a separate installation operation for each line, done with a wrench that swings over a wide arc perpendicular to the line. There is less and less underhood room available for such installation operations. Often, two of the lines run perpendicular to each other, which requires even more space. Other designs use a separate bolt to connect each of the four lines, which bolts are oriented parallel to the lines. Such bolts can be attached with a power socket driver that does not swing wide of the line, but four separate bolts still require a significant installation time.
Other block connector designs reduce the number of installation operations by connecting at least two of the four lines simultaneously to the block, as a yoked pair held in position by an anchor plate. The plate is pulled tight to the side of the block with a threaded bolt or pair of bolts. In one design, only the compressor and condenser lines are attached by an anchor plate, while the evaporator lines are permanently brazed into the other side of the block. As noted, permanent connections are undesirable because they cannot be disassembled. In another design, only the evaporator lines are attached to the block by a bolt and anchor plate, while the compressor lines are still connected with separately installed threaded fittings. In designs where all four of the lines are connected in two pairs by two bolted on anchor plates, separate bolts are generally used for each plate. In one such two anchor plate design, short bolts attached from opposite sides of the block attach the two plates. Since block access from the evaporator side is often limited or difficult, other two plate designs run all the bolts from the compressor side of the block. In one example, a first anchor plate attaches the two evaporator lines using a pair of threaded bolts long enough to run all the way through the block, side to side, with the bolt heads inset into the block. Then, a second plate, holding the compressor-condenser lines, is attached by its own, single, shorter threaded bolt, thereby covering up the inset heads of the first two, longer bolts. This presents the obvious disadvantage of being unable to check on or tighten the first two bolts once the last anchor plate has been added. There are three bolts to potentially loosen, only one of which is easily accessible. The obvious expedient of using common threaded bolts to run through both plates and sandwich the block between, while it would make the heads of the bolts always accessible from the compressor side of the block, is undesirable. This would make it impossible to remove the compressor side anchor plate independently of the evaporator side anchor plate. Furthermore, bolts long enough to reach all the way through the block (and through both plates) would be subject to misalignment relative to the two plates' bolt holes.